----- Original Message ----- From: "ZN" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, July 14, 2005 2:53 PM Subject: Re: [ql-users] Size for QXL.win Files
> On 08/07/05 at 11:23 P Witte wrote: > > >> John Gilpin writes: > >> 4Gb per QXL.win file... > > >I only get 2GB with QPC2: FORMAT win8_4000 fails while win8_2000 doesnt. > >Even then the file allocation block is a massive 32k. It seems to me that > >4GB must be the theoretical limit for the current mapping scheme. The > >minimum space taken by a file on disk would then be a whopping 64k > > > >Per > > Per is right, IIRC QLWA may have a 2G limit, even though 4G would be the > theoretical maximum. > There are two possible reasons for it: > 1) Maximum number of allocation blocks (think of them as a sort of > super-sector) is a 16 bit word, unfortunately, some implementations and > versions took it a s a signed integer instead of unsigned. > 2) Maximum size of one allocation block is a 16 bit word, again some > implementations and versions used signed arithmetic to point to a byte > within the block, which reduces it's maximum size to 32k. > IIRC the first error is the more likely to crop up. When QUBIDE was being > maintained, these cropped up, but I do not remember the speciffics any > more. > 4G is a sort of double limit as the system implies that the whole QLWA > partition can be used up by a single file. Since the file pointer is a 32 > bit unsigned (hopefully!) integer, the maximum size of a file is 4G, and so > is the size of the partition (64k blocks each 64k in size = 4G). > The serious limitiation here is that one file always takes up at least 1 > allocation block (even if the file is empty!) and the less serious one is > that there can be max 64k files. The first is quite restrictive in QL terms > as files are, in general, much shorter than 64k. This produces a lot of > wasted space. > If you want to be absolutely sure, 1G QXL.WIN, with 32k allocation block > size is the way to go, it avoids all the possible pitfalls... > > Nasta > Thanks for the advice, Nasta, and all explained so that I can follow the reasoning. I will do a bit of experimenting but the comments received as to what should be theoretically achievable is a great help. John Gilpin. _______________________________________________ QL-Users Mailing List http://www.q-v-d.demon.co.uk/smsqe.htm
